Blood testing tool

A blood testing tool, comprising an asymmetric porous membrane with a pore size distribution in which an average pore size varies so that it is reduced continuously or discontinuously in a thickness direction,

• wherein the asymmetric porous membrane includes a blood supply portion, a development portion, and a blood-cell blocking portion formed between the blood supply portion and the development portion, pores in the blood-cell blocking portion include only pores through which blood cells cannot pass, the arrangement being such that when blood is supplied to the blood supply portion at a side having larger pores, the blood moves in a direction substantially parallel to a surface of the asymmetric porous membrane by capillary action, and when the blood reaches the blood-cell blocking portion, the movement of blood cells in a direction substantially parallel to the surface is blocked, such that only blood plasma or blood serum moves into the development portion.